It was recently demonstrated by George et al. that in some chronically depressed patients, rTMS (rapid transcranial magnetic stimulation) of the left forebrain reduced their feelings of sadness significantly (as measured by the Hamilton index). rTMS is painless and free of the stigma associated with electroconvulsive therapy (ECT). Moreover, it was found that convulsions did not have to be induced in order to produce a favorable clinical outcome. Bioengineering contributions to this project from our group involved (a) the original suggestion that rTMS could be used as a potential therapeutic modality, and (b) the determination of efficacious and safe levels of rTMS in clinical trials, both with normal volunteers and with depressed patients. Modeling efforts are under way to quantify the electromagnetic "dose" of different rTMS protocols so that they can eventually be correlated to patient "response."